How to balance fan blades?

[7_Zero]

In an effort to better educate ourselves and others, our club encourages its members to research a topic and do a presentation or write an article about that topic. There has been a lot of talk about the dangers of failing fans, and since I believe most of our club members are running original fans, I thought I would do an article about the Model A fans.

A key factor to a smooth operating and long lasting fan is balance. I have not had to balance a fan so I am at a loss as to the best approach is for this. I have read a few articles ranging from balancing mower blades, boat props and aircraft propellers. The methods vary from grinding material from the leading edge or tip of the blade, sanding or polishing the face of a blade, adding weight or even just adding an extra coat of paint to the light end. Some methods I feel would not be appropriate for a Model A fan.

To those of you who are more knowledgeable about this, which, if any, method would be the most appropriate to balance a fan? Any direction or insight would be much appreciated!
Thanks!

[J Franklin]

There are low priced blade balancers for mower blades that I've seen at hardware and farm stores, they should do the job. I would take weight off the heavy side by filing or grinding.

[Mike V. Florida]

While worthwhile to give one a sense of security, I have never seen a method in print. Since it spins like a mower blade I would think a mower blade balancer like mentioned above, would work. I would only remove material, never add.

[BRENT in 10-uh-C]

Actually while it is probably better to do it dynamically, it can be done statically using a set of knife edges on either a balanced mandrel or a water pump shaft. Remove weight from the tips.

[Bob Bidonde]

You can balance a fan using a wheel bubble balancer. Better yet, install an electric fan.



Never, never, never, never us an original 2-blade fan, no matter how pretty it looks, because there is no way of determine its remaining fatigue life. Disregard this advice and this will likely happen!

[WHN]

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Originally Posted by Bob Bidonde

You can balance a fan using a wheel bubble balancer. Better yet, install an electric fan.



Never, never, never, never us an original 2-blade fan, no matter how pretty it looks, because there is no way of determine its remaining fatigue life. Disregard this advice and this will likely happen!

Been there, done that!

However, I have had really good luck with the new two blade aluminum fan blades.

If you are running orginal blade, I would remove it as soon as possible.

[duke36]

Ditto to Bob B and WHN; go a bit farther and not use the 4 blade metal with rivets and/or bolts. Had 2 with bad hairline cracks near the hub obscured by paint !

[Jungle Jim]

Years ago I worked for Canadian Fram where we made automotive cooling fans and they dynamically balanced the blades and punched the hole in the optimum location.

Jim

[Tom Endy]

The photos are of the static balancer a friend of mine built about 20 years ago. He was a WWII B-17 bomber pilot and spent most of his life as a commercial airline pilot. His hobby was radio controlled model airplanes. The balancer was originally designed to balance model airplane propellers, but since he was also into Model A’s he found that it did a reasonably good job of balancing Model A fans. Some of the early cast aluminum fans were way out of balance and he was able to bring them into balance by grinding material off the heavy blade.

One night he and I took the balancer to a club meeting along with a number of fans to demonstrate the value of the balancer. At the time we had a club member who was an expert on everything, and he didn’t mind telling you he was. In the middle of our presentation he began loudly telling everyone that a static balancer was a worthless piece of junk, and that electronic dynamic balancing was the only proper way to balance a fan.

We quietly folded our presentation and put the balancer back in the car. It has never been seen at a club meeting since. However, a number of club members over the years have brought Model A fans to us and asked us to balance them.


I apologize to the fordbarn forum if I am leading anyone astray; if I am, my advice then is to have your Model A fan balanced at one of those electronic dynamic balancing stores in your neighborhood.

Tom Endy

[7_Zero]

Thank you all for your replies!

Brent, do you find static balancing gets it close enough, or is it worth while to go the extra step and get it dynamically balanced? I have heard that the cost to dynamically balance a fan can cost more than the fan itself. Maybe I am looking in the wrong place?

Duke, are you suggesting that even the new 4 blade fans should be avoided? Or just the older ones?

Tom, there always seems to be at least one of those people in the group who ruin it for everyone else.

[BILL WILLIAMSON]

Every club has its' SMART ASSED "EXPURT"!
When I was describing my GREAT 10 Fin Radiator & Fan, he said, "With all that GREAT stuff, HOW do you warm it up in the WINTER"?-----"I have a THERMOSTAT, DUMB ASS"!!---"What did you think I did, build a FIRE in it"?
Bill W.

[Simonpie]

Dynamic balancing of anything is important if the item is long along the shaft, like a crank. They dynamically balance car tires because they are getting pretty wide nowadays, i.e. long along the shaft. Motorcycles are usually statically balanced. Some bike shops have dynamic balancers, but this is usually because they are fast, and time is money. Many race tire vendors use a simple ball bearing axle static balance. There is no reason to dynamically balance a fan.
If your concern is a fan blade flying off, there is also no reason to balance the fan at all. Each blade is pulling with the same full force based on the weight, distance from center, and rpm. Balancing matches one blade force to the opposite, but doesn't reduce the fundamental pull on the blade at all. The fatigue load of the fan blade would primarily be in bending from aerodynamic forces as the blade crosses across open radiator and then into air shrouded by the block and head. It doesn't seem like much, but the fan is thin in bending in the fore-aft direction (except the aluminum ones). There isn't much you can do about this loading. If your concern is pump shaft life or smooth running, by all means balance it.
If you want a cheat to increase fan life, run a bigger crank pulley. This will slow the fan and reduce loads. It will also reduce cooling and your generator output, and be hard to fit, so be warned.

[Synchro909]

Originally Posted by Simonpie

If you want a cheat to increase fan life, run a bigger crank pulley. This will slow the fan and reduce loads. It will also reduce cooling and your generator output, and be hard to fit, so be warned.

Unless things work differently upside down over there, increasing the carnk pulley would increase the speed of water pump and generator by my reconning.

[Simonpie]

Originally Posted by Synchro909

Unless things work differently upside down over there, increasing the carnk pulley would increase the speed of water pump and generator by my reconning.

D'oh! You're right.
That fixes the "harder to install" issue as well.

[BILL WILLIAMSON]

Originally Posted by Simonpie

D'oh! You're right.
That fixes the "harder to install" issue as well.

Reminds me of Chief & Uncle "Pappy", they would drain the oil in Grandpas' Model T, then roll it on its' SIDE, to pull off the oil pan!
Chiefs' Son, Bill W.